Fix merging of selected streams.

Playback would fail if a renderer is toggled from consuming from
one child to another in a single step.

Issue: #1900

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=135270356

RELEASENOTES.md

@@ -4,7 +4,8 @@
 
 
 * Fixes for MergingMediaSource and sideloaded subtitles.
 * Fixes for MergingMediaSource and sideloaded subtitles.
   ([#1882](https://github.com/google/ExoPlayer/issues/1882),
   ([#1882](https://github.com/google/ExoPlayer/issues/1882),
-  [#1854](https://github.com/google/ExoPlayer/issues/1854)).
+  [#1854](https://github.com/google/ExoPlayer/issues/1854),
+  [#1900](https://github.com/google/ExoPlayer/issues/1900)).
 * Reduced effect of application code leaking player references
 * Reduced effect of application code leaking player references
   ([#1855](https://github.com/google/ExoPlayer/issues/1855)).
   ([#1855](https://github.com/google/ExoPlayer/issues/1855)).
 * Initial support for fragmented MP4 in HLS.
 * Initial support for fragmented MP4 in HLS.

library/src/main/java/com/google/android/exoplayer2/source/MergingMediaPeriod.java

@@ -85,7 +85,8 @@ import java.util.IdentityHashMap;
       }
       }
     }
     }
     streamPeriodIndices.clear();
     streamPeriodIndices.clear();
-    // Select tracks for each child, copying the resulting streams back into the streams array.
+    // Select tracks for each child, copying the resulting streams back into a new streams array.
+    SampleStream[] newStreams = new SampleStream[selections.length];
     SampleStream[] childStreams = new SampleStream[selections.length];
     SampleStream[] childStreams = new SampleStream[selections.length];
     TrackSelection[] childSelections = new TrackSelection[selections.length];
     TrackSelection[] childSelections = new TrackSelection[selections.length];
     ArrayList<MediaPeriod> enabledPeriodsList = new ArrayList<>(periods.length);
     ArrayList<MediaPeriod> enabledPeriodsList = new ArrayList<>(periods.length);
@@ -106,22 +107,20 @@ import java.util.IdentityHashMap;
         if (selectionChildIndices[j] == i) {
         if (selectionChildIndices[j] == i) {
           // Assert that the child provided a stream for the selection.
           // Assert that the child provided a stream for the selection.
           Assertions.checkState(childStreams[j] != null);
           Assertions.checkState(childStreams[j] != null);
-          streams[j] = childStreams[j];
+          newStreams[j] = childStreams[j];
           periodEnabled = true;
           periodEnabled = true;
           streamPeriodIndices.put(childStreams[j], i);
           streamPeriodIndices.put(childStreams[j], i);
         } else if (streamChildIndices[j] == i) {
         } else if (streamChildIndices[j] == i) {
           // Assert that the child cleared any previous stream.
           // Assert that the child cleared any previous stream.
           Assertions.checkState(childStreams[j] == null);
           Assertions.checkState(childStreams[j] == null);
-          if (selectionChildIndices[j] == C.INDEX_UNSET) {
-            // No other child will be setting the stream at index j, so clear it.
-            streams[j] = null;
-          }
         }
         }
       }
       }
       if (periodEnabled) {
       if (periodEnabled) {
         enabledPeriodsList.add(periods[i]);
         enabledPeriodsList.add(periods[i]);
       }
       }
     }
     }
+    // Copy the new streams back into the streams array.
+    System.arraycopy(newStreams, 0, streams, 0, newStreams.length);
     // Update the local state.
     // Update the local state.
     enabledPeriods = new MediaPeriod[enabledPeriodsList.size()];
     enabledPeriods = new MediaPeriod[enabledPeriodsList.size()];
     enabledPeriodsList.toArray(enabledPeriods);
     enabledPeriodsList.toArray(enabledPeriods);

library/src/main/java/com/google/android/exoplayer2/source/hls/HlsMediaPeriod.java

@@ -39,6 +39,7 @@ import com.google.android.exoplayer2.upstream.Allocator;
 import com.google.android.exoplayer2.upstream.DataSource;
 import com.google.android.exoplayer2.upstream.DataSource;
 import com.google.android.exoplayer2.upstream.Loader;
 import com.google.android.exoplayer2.upstream.Loader;
 import com.google.android.exoplayer2.upstream.ParsingLoadable;
 import com.google.android.exoplayer2.upstream.ParsingLoadable;
+import com.google.android.exoplayer2.util.Assertions;
 import java.io.IOException;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.ArrayList;
 import java.util.IdentityHashMap;
 import java.util.IdentityHashMap;
@@ -154,7 +155,8 @@ import java.util.List;
     }
     }
     boolean selectedNewTracks = false;
     boolean selectedNewTracks = false;
     streamWrapperIndices.clear();
     streamWrapperIndices.clear();
-    // Select tracks for each child, copying the resulting streams back into the streams array.
+    // Select tracks for each child, copying the resulting streams back into a new streams array.
+    SampleStream[] newStreams = new SampleStream[selections.length];
     SampleStream[] childStreams = new SampleStream[selections.length];
     SampleStream[] childStreams = new SampleStream[selections.length];
     TrackSelection[] childSelections = new TrackSelection[selections.length];
     TrackSelection[] childSelections = new TrackSelection[selections.length];
     ArrayList<HlsSampleStreamWrapper> enabledSampleStreamWrapperList = new ArrayList<>(
     ArrayList<HlsSampleStreamWrapper> enabledSampleStreamWrapperList = new ArrayList<>(
@@ -168,19 +170,23 @@ import java.util.List;
           mayRetainStreamFlags, childStreams, streamResetFlags, !seenFirstTrackSelection);
           mayRetainStreamFlags, childStreams, streamResetFlags, !seenFirstTrackSelection);
       boolean wrapperEnabled = false;
       boolean wrapperEnabled = false;
       for (int j = 0; j < selections.length; j++) {
       for (int j = 0; j < selections.length; j++) {
-        if (selectionChildIndices[j] == i
-            || (selectionChildIndices[j] == C.INDEX_UNSET && streamChildIndices[j] == i)) {
-          streams[j] = childStreams[j];
-          if (childStreams[j] != null) {
-            wrapperEnabled = true;
-            streamWrapperIndices.put(childStreams[j], i);
-          }
+        if (selectionChildIndices[j] == i) {
+          // Assert that the child provided a stream for the selection.
+          Assertions.checkState(childStreams[j] != null);
+          newStreams[j] = childStreams[j];
+          wrapperEnabled = true;
+          streamWrapperIndices.put(childStreams[j], i);
+        } else if (streamChildIndices[j] == i) {
+          // Assert that the child cleared any previous stream.
+          Assertions.checkState(childStreams[j] == null);
         }
         }
       }
       }
       if (wrapperEnabled) {
       if (wrapperEnabled) {
         enabledSampleStreamWrapperList.add(sampleStreamWrappers[i]);
         enabledSampleStreamWrapperList.add(sampleStreamWrappers[i]);
       }
       }
     }
     }
+    // Copy the new streams back into the streams array.
+    System.arraycopy(newStreams, 0, streams, 0, newStreams.length);
     // Update the local state.
     // Update the local state.
     enabledSampleStreamWrappers = new HlsSampleStreamWrapper[enabledSampleStreamWrapperList.size()];
     enabledSampleStreamWrappers = new HlsSampleStreamWrapper[enabledSampleStreamWrapperList.size()];
     enabledSampleStreamWrapperList.toArray(enabledSampleStreamWrappers);
     enabledSampleStreamWrapperList.toArray(enabledSampleStreamWrappers);